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From 1987 to 1993 we assessed the variation of phytoplankton biomass, underwater irradiance and primary production in Lake
Xolotlán (L. Managua, Nicaragua). Chlorophyll- a averaged 65 mg m-3 and maximum and minimum concentrations were 120 and 30
mg m-3, respectively. The variability over depths and weeks was low (CV < 20%). There were strong correlations between particulate
carbon and chlorophyll- a (the ratio ≈ 100: 1) and between particulate carbon and particulate nitrogen and phosphorus (the
ratio ≈ 100: 11: 1). Gross primary production averaged 6.8 g C m-2 d- 1 and was stable over the years (CV ≈ 10%). Algal cell
growth was approximately 4–5 g C m-2 d- 1. Productivity was limited only by the availability of underwater light and the depth
of the photic zone was mainly regulated by the chlorophyll- a concentration. Therefore, areal photic zone chlorophyll- a was
the only factor directly correlated to the integral photosynthetic activity but, contrary to theoretical models, the production
did not increase in proportion to chlorophyll- a. Data from African lakes show a similar pattern.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Lene Vammen S?ndergaard Jan Ladewig Frederik Dagn?s-Hansen Mette S. Herskin Ida Elisabeth Holm 《Transgenic research》2012,21(6):1341-1348
Alzheimer??s disease (AD) is a disabling, fatal disease, where animal models potentially can enable investigation of aetiology and treatment. The first litter of G?ttingen minipigs carrying a mutation for human AD was born in 2007, showing transgene expression. In human AD patients, memory impairment is the most striking and consistent feature. The aim of the present study was to examine effects of the APPsw transgene on memory of AD minipigs compared with non-transgenic controls at two ages (1?C2?years) using the spontaneous object recognition test (SORT), which is based on behavioural discrimination of familiar and novel objects. No significant difference between AD minipigs and controls was found when comparing object recognition as a measure of memory. The minipigs did explore the novel object significantly more than the familiar, indicating the expected recognition of the familiar object. Two different inter-phase intervals were used (IPI: 10?C40?min). For both ages, object recognition was evident using 10?min IPI. When using 40?min IPI, object recognition was evident only at age 1?year. Comparing memory of a relatively small group of AD minipigs and controls at two rather young ages using the SORT, we were not able to show memory impairment in APPsw carrying minipigs. Being an age-dependent disease, the transgene is expected to cause AD-like symptoms in this porcine model, and the SORT should be repeated at older ages. 相似文献
3.
An integral view of the trophic aspects so far obtained from studies of phytoplankton, zooplankton, benthos and fish in Lake Xolotlán (Managua) is presented as a first contribution to the analysis of the lake ecosystem. 相似文献
4.
Russell T. Bell Rolf Erikson Kathleen Vammen Maria Helena Vargas Argentina Zelaya 《Aquatic Ecology》1991,25(2):145-149
The biomass and production (thymidine incorporation) of heterotrophic bacterioplankton has been assessed from July, 1988, to October, 1989. in Lake Xolotlán, Nicaraqua. Bacterial abundance was high, 2–3.1010 cells.l–1, and bacterial biomass averaged ca. 0.75 mg C.l–1, or roughly 20% of the partivculate organic carbon. Bactrial production averaged between 3.5–5 g C.l–1.h–1 and on a areal basis was 650–959 mg C.m–2.d–1 or 13–20% ofthe primary production. Although bacterial production (volumetric basis) was typical for eutrophic lakeks, the bacterial specific growth rate was low, the bacteial population doubling time was ca. 1 week, perhaps indicating that there was a low grazing pressure on the bacteria. 相似文献
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From 1988 to 1993 we assessed the variability of bacterioplankton production and biomass in Lake Xolotlán (L. Managua), Nicaragua
via [3H]thymidine incorporation into DNA and cell counting. Bacterial production ranged from 3 to 8 μg C l-1 h-1, and since
production was equal throughout the water column, areal production was high (≈ 600–1200 mg C m-2 d-1). Bacterial abundance
in Lake Managua was extremely high, 7–30 × 109 cells l-1. Thus, specific rates of bacterial production were low. There was
a strong correlation between production and number and the specific rate of bacterial production was constant. Comparable
measurements of production via [3H]leucine incorporation into proteins indicated that bacteria were experiencing ‘balanced
growth’. We conclude that bacterioplankton in Lake Xolotlán had reached its carrying capacity and a significant correlation
between bacterial production and concentration of phaeophytin implied that dead or dying algae was the limiting substrate
for bacterioplankton. The majority of bacterial number and most of bacterial production (up to 75%) were associated with particles
in the >3-μm fraction, probably lysing algal cells to which bacterioplankton were ‘attached’. Grazing on bacterioplankton
must be low and bacteria should be a ‘sink’ for organic matter in Lake Xolotlán.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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